A huge number of separate regions where Big Bangs occur are separated by continuously inflating space in eternal inflation. In order for our Universe to exist, it must have a finite probability of creation, given a multiverse. Image credit: Karen46 of FreeImages.

“Logic takes care of itself; all we have to do is to look and see how it does it.” -Ludwig Wittgenstein

There are a great many events that occurred to give rise to the world, the Universe, and you. Everything from the Big Bang to the existence of the laws of physics to the cosmic history that created Earth to the biological history that gave rise to the 7+ billion of us today needed to unfold exactly as it did in order for things to be the way they are today.

A standard cosmic timeline of our Universe’s history. A series of extremely unlikely events all needed to occur in order so that you would exist. Image credit: NASA / CXC / M. Weiss.

It’s an exceedingly unlikely story, and yet the fact that we’re here is evidence that it happened exactly in this fashion. But no matter how unlikely it appears, we can be 100% certain that our arrival at this point in time with these exact conditions wasn’t infinitely unlikely. In fact, it’s an inescapable consequence of Bayes’ theorem that the existence of things as they are today implies it had a finite, not infinitesimal, probability of turning out this way.

One of the most fundamental and useful rules in probability is Bayes’ theorem, mathematically expressed in blue neon at the offices of Autonomy in Cambridge. Image credit: mattbuck of Wikimedia Commons.